1. Field of the Invention
The invention relates to an heat exchange device for adjusting the temperature of a liquid and, in particular, for cooling blood in order to induce cardioplegia during coronary surgery.
2. Description of the Related Art
The invention is described in connection with the cooling of blood for inducing cardioplegia during coronary surgery. However, it is to be understood that this particular example is given purely by way of illustration and is not intended to limit the scope of the invention as claimed.
During cardiac vascular surgeries and valvular surgeries it is necessary to arrest the pumping activity of the heart. This is usually accomplished by delivering a hypothermic solution of potassium and the patient's blood to the patient in order to cause cardioplegia (heart paralysis). The hypothermic solution can be administered antigrade directly into the coronary ostia or retrograde through the right atrium or the coronary sinus, depending upon surgical need. The hypothermic solution is generally cooled in a heat exchange device which may include a dedicated heater/cooler device or an ice bath.
There are generally two varieties of cardioplegia heat exchange devices that are commercially available. The first variety includes a cooled and/or heated water bath into which a heat exchange element is immersed. In the second variety, a heater/cooler device circulates temperature controlled fluid, such as water around a heat exchange element through which blood passes.
There are a number of drawbacks with the devices currently available. First, a lack of cooling efficiency in some devices can result in too high a myocardial temperature, causing ischemia during the period of cardioplegia administration, which in turn can cause heart tissue damage. Another drawback of related art devices is that temperature may be difficult to precisely control, especially in devices where pockets of coolant can stagnate, leading to differences in coolant temperatures within the device.
A further problem with related art devices is that they tend to be non-compact in size and shape and can be difficult to set up and use.
Finally, some devices have blood flow paths that cause difficulties in eliminating air bubbles and maintaining non-turbulent blood flow. This can be very dangerous because air bubbles released into the patient's circulatory system can cause disastrous results. Further, turbulent blood flow within the cooling device can result in blood trauma and blood cell damage.